This invention relates generally to disconnect switches, and, more particularly, to fused disconnect switches.
Fuses are widely used as overcurrent protection devices to prevent costly damage to electrical circuits. Fuse terminals typically form an electrical connection between an electrical power source and an electrical component or a combination of components arranged in an electrical circuit. One or more fusible links or elements, or a fuse element assembly, is connected between the fuse terminals, so that when electrical current through the fuse exceeds a predetermined limit, the fusible elements melt and opens one or more circuits through the fuse to prevent electrical component damage.
In some applications, fuses are employed not only to provide fused electrical connections but also for connection and disconnection, or switching, purposes to complete or break an electrical connection or connections. As such, an electrical circuit is completed or broken through conductive portions of the fuse, thereby energizing or de-energizing the associated circuitry. Typically, the fuse is housed in a fuse holder having terminals that are electrically coupled to desired circuitry. When conductive portions of the fuse, such as fuse blades, terminals, or ferrules, are engaged to the fuse holder terminals, an electrical circuit is completed through the fuse, and when conductive portions of the fuse are disengaged from the fuse holder terminals, the electrical circuit through the fuse is broken. Therefore, by inserting and removing the fuse to and from the fuse holder terminals, a fused disconnect switch is realized.
Known fused disconnect switches of this type, however, are disadvantaged in certain applications. For instance, in telecommunications applications, increasing power demands of equipment loads have rendered many fused disconnect switches inadequate. In addition, limited field wiring options can frustrate the use of a common line input bus and may require auxiliary components for connection to telecommunication distribution panels. Still further, especially when a large number of disconnect switches are employed, quick and accurate identification of opened fuses is necessary so that opened fuses may be identified and replaced. Conventional fuse state identification mechanisms are not as reliable as desired for telecommunications applications. For at least the above reasons, use of fused disconnect switches have not completely met the needs of certain end applications, such as use in telecommunications systems.
In an exemplary embodiment, a fused disconnect switch assembly includes a pull out fuse assembly and a switch housing assembly. The fuse assembly includes a line side conducting portion, a load side conducting portion, and a fuse element therebetween. The switch housing assembly includes a housing defining a fuse receptacle for receiving the fuse, a first contact assembly located in the housing and coupled to the line side conducting portion of the fuse when the fuse is inserted into the receptacle, and a second contact assembly located in the housing and coupled to the load side conducting portion of the fuse when the fuse is inserted into the receptacle. An open fuse indication device is in communication with the line side conducting portion of the fuse and the load side conducting portion of the fuse, and an alarm terminal output extends from the switch assembly housing and is in communication with the open fuse indication device. The open fuse indication device provides local fuse state indication and the alarm terminal output facilitates remote fuse state indication when coupled to external circuitry in the end application.
In various embodiments, the switch housing assembly includes a bullet contact assembly, a box contact assembly, and a terminal stud for increased wiring options in the field. A common contact bus bar is provided for connection to a terminal stud in one embodiment for further wiring options and auxiliary connections.
In an exemplary embodiment, the fuse line side conducting portion and fuse load side conducting portion includes terminal blades that are extended through terminal openings extending through a bottom of the fuse receptacle. The terminal blades are engaged to the terminal contact assemblies of the switch housing assembly. The open fuse indication device includes a high resistance electronic circuit coupled to the terminal blades of the fuse, and the circuit includes a transistor element and an light emitting diode (xe2x80x9cLEDxe2x80x9d). The LED is activated by the transistor element in response to a voltage drop across the electronic circuit. The switch housing further includes an internal alarm terminal engaging an alarm terminal of the fuse within the fuse receptacle, and further in communication with the alarm output terminal The open fuse indication device therefore provides local fuse state indication via illumination of the LED and generates an alarm signal that is output through the switch housing alarm output for remote fuse state identification.
A fused disconnect switch is therefore provided with a variety of wiring options including a common bus connection, without employing auxiliary components. Reliable local and remote fuse state indication is provided so that opened fuses may be quickly identified and replaced. A versatile, compact fused disconnect switch package is therefore provided that is better suited for applications wherein conventional fused disconnect switches have been found less than desirable, such as telecommunications applications.